1. Field of the Invention
The invention relates to electric servomotors, particularly with respect to monitors therefor.
2. Description of the Prior Art
Servomotors are prevalent in various technologies for positioning output members in accordance with input command signals. Servomotors, for example, are utilized in automatic flight control systems for aircraft for positioning the aerodynamic control surfaces such as the ailerons, elevators and rudders as well as for positioning the engine throttles. Traditionally, feedback paths are utilized around such servomotors for providing, for example, motor damping. In a damping feedback loop, a tachometer generator coupled to the motor output shaft provides a feedback signal proportional to the rate of rotation of the motor. Since safety and reliability are of paramount importance in the design of automatic flight control systems, dangerous failures such as servomotor hardover or oscillatory conditions resulting from servo feedback faults must be obviated. In prior art, automatic flight control system servoes redundant feedback paths are utilized. In such configurations, dual tachometer generators are coupled to the servomotor output shaft with the rate feedback signals from the tachometers being combined for utilization as the servo feedback signal. Monitoring circuitry is included for comparing the outputs of the dual tachometers with facility for disabling the servo should a miscomparison occur.
It is a desideratum of automatic flight control system design to elminate as many heavy, bulky and expensive components of the flight control system as practicable without reducing safety margins and reliability. The tachometer generator typically utilized in the servo motor feedback loops is such a component and elmination of the redundancy thereof is desirable.